Under certain circumstances, congressional committee staff members may choose to depose potential witnesses and scheduled witnesses. The purpose of such depositions is to gather information in order to prepare for a hearing. This is more common in investigative hearings.

Formal in nature, such questioning of a witness is the equivalent of taking testimony in private. The deposition may be administered under oath and may also include advanced written questions as well as a full transcript. In most instances, deposed witnesses will be accompanied by legal counsel.

Any witness that is called for a deposition should ensure they have a clear understanding regarding the purposes as well as the authority for the deposition. It is often a good idea to consult legal counsel to obtain advice regarding the substance and procedure of the deposition. This will also help to ensure that the constitutional rights of the witness are protected. The practices of committees regarding depositions can vary significantly.

Witnesses who are called to testify before a congressional committee should fully understand that they have basic rights and protections provided under the U.S. Constitution and to rights provided under rules that are adopted by the Senate and the House and their committees. Basic constitutional rights include First Amendment rights to free speech, assembly and petition; Fourth Amendment rights against unreasonable search and seizure to obtain documents or information; and Fifth Amendment rights against self-incrimination. This includes protection against being compelled to provide testimony against oneself that might be incriminating.

Under House and Senate rules, added protections include the right to legal counsel, the right to have counsel present to provide legal advice, the right to request that television cameras be turned off, and, in some cases, the right to refuse to be photographed. In certain circumstances, witnesses may also have the right to request that hearings be closed.

The protocol regarding the use of legal counsel during a hearing falls within the purview of each individual committee. As a result, witnesses who would like to bring legal counsel to a hearing should first consult with the relevant committee staff. In most cases, legal counsel is not necessary, but when an investigative hearing is involved and when a witness has been subpoenaed or requested to submit to a deposition, legal counsel is more frequently involved.